What are the main hazards of ultraviolet rays to liquid silicone?

What are the main hazards of ultraviolet rays to liquid silicone?
Accelerated aging
Molecular chain breakage: Ultraviolet rays have high energy. When liquid silicone is exposed to ultraviolet radiation for a long time, ultraviolet rays can destroy the chemical bonds in the silicone molecular chain and cause it to break. For example, key chemical bonds such as silicon-oxygen bonds (Si-O) will gradually be destroyed under the continuous action of ultraviolet rays, causing the originally long polymer chains to break into shorter segments. As the molecular chains continue to break, the molecular weight of liquid silicone decreases, which in turn causes changes in its various physical properties.
Performance degradation: This change caused by the breakage of molecular chains will make liquid silicone hard and brittle, and its flexibility and elasticity will be greatly reduced. Liquid silicone that can be bent and stretched at will will easily break and crack after aging, and can no longer meet some application scenarios with high flexibility requirements. For example, the use of flexible electronic devices and sealing gaskets will be restricted. At the same time, the tear strength will also be significantly weakened, and it is more likely to be damaged when pulled by external forces.
Appearance changes
Discoloration: UV radiation can easily cause liquid silicone to change color. This is because UV radiation interacts with some additives in silicone or its own chemical structure, triggering chemical reactions such as oxidation. For example, some originally colorless and transparent liquid silicone may gradually turn yellow or brown after long-term UV radiation, affecting its appearance and transparency. For products with high appearance requirements, such as silicone accessories, transparent food-grade silicone tableware, etc., it no longer meets the use requirements.
Surface powdering: Under the influence of ultraviolet rays for a long time, the surface of liquid silicone may also powder. After the molecular structure of its outer layer is destroyed, it will gradually decompose to form fine powdery substances, making the surface of the silicone no longer smooth and flat, but rough, which not only affects the appearance, but also these powders may contaminate other objects or environments in contact with it after falling off.
Affecting the curing effect
Uneven curing: During the curing process of liquid silicone, if it is interfered by ultraviolet rays, it may cause uneven curing. Because the energy distribution of ultraviolet rays may cause the silicone molecules in local areas to be activated prematurely or the reaction degree to be inconsistent. For example, when performing the light curing process (some special liquid silicones use light curing), factors such as the angle and intensity of ultraviolet rays can easily cause different parts of the silicone to cure faster or slower, resulting in quality problems such as uneven surface and incompletely cured parts inside, affecting the quality and performance of the final silicone products.
Incomplete curing: In severe cases, the damage of ultraviolet rays to the chemical substances involved in the curing reaction may prevent the curing reaction from being completed according to the normal process, resulting in incomplete curing, causing the silicone to be unable to form a stable cross-linked structure, and the performance indicators such as hardness and strength of the product cannot meet the expected standards. It is also easy to become sticky and cannot be put into use normally.